Cranes that move on steel rails installed on the ground or on elevated runways are used to transport objects and materials from one location to another. Examples include industrial buildings (steel mills) and ports where ships are unloaded and goods are placed on transport vehicles. The rails are called crane rails and are required to safely support heavy loads while maintaining a low maintenance, extended life cycle. Compared to the common “Tee-rails” used for railroads and light rail transit lines, crane rails typically have significantly more massive head sections and thicker web sections.
As loads have increased over the years, the crane rail must resist plastic deformation and damage. The current trend is that the crane rail must have higher hardness and high strength to resist damage. A typical industrial crane (steel mill) has eight wheels, 60-70 cm in diameter with wheel loads up to 60 tons. The point of actual contact between a steel crane rail and the crane wheel is quite small and usually concentrated in the center of the crane rail head. Since both the rail and wheel are at a high level of compression; very large localized stresses result. Recently many cranes have switched to harder wheels to extend wheel life and to lower maintenance costs. The moving crane and the accompanying shock loads can result in fatigue damage to the crane rail, the wheel and the supporting girder system. Crane rails are also subject to head wear and are routinely inspected to determine that the amount of wear is still acceptable for continued use. It is necessary to replace the crane rail when it suffers mushrooming or non-symmetrical deformation and wear.
Based on increasing crane loads and higher hardness crane wheels, the crane rail technical requirements in general are shifting to higher hardness, higher strength steel grades. Because of the limited size of the crane rail market, there are few steel mills that produce crane rails, leaving customers in a difficult situation.
The ArcelorMittal Steelton plant is the major producer of crane rails in the Western Hemisphere and has utilized its rail head hardening facility to produce a higher hardness crane rail by accelerated cooling directly off the rail mill. However, customers are requesting even higher hardness crane rail for heavy load applications than are available from conventional rail steel compositions. There is a need in the art for a high hardness crane rail having a higher hardness than is presently conventionally available.